1. Field of the Invention
The present invention relates to a ball bearing and a lubricating method thereof, in particular, the ball bearing which has a resistance against a fretting characteristic when non-rotating and a lubricating property when rotating by disposing greases different in property respectively, and a lubricating method thereof.
2. Related art
In general, a ball bearing is lubricated by being applied with a grease, as shown in FIG. 3, within the bearing between an outer race 1 and an inner race 2, and a torque transmittance property of the ball bearing and the resistance property against fretting depends on the property of the grease to be applied. For reference, in a use of a spindle motor for HDD (hard disk drive) which is required to give a low torque and a low noise, a churning type of grease having a basic oil viscosity of 25˜35 mm2/s and a worked penetration of 240˜270 is mainly used. Further, the grease of this type is superior in a property of maintaining a rolling life at the time of rotation of the bearing.
However, this grease of this type is not effective for protecting a contact surface of the inside of the bearing from the fretting generated at the time of non-rotation of the bearing, and in general, it has been known that a churning type of grease having a basic oil viscosity of 15˜20 mm2/s and a worked penetration of 200˜230 is superior in a resistance property against a fretting at the time of non-rotation of the bearing.
This is because, on one hand, a basic oil having a high viscosity is easily to be excelled from a contacting surface between balls 3 and rolling surfaces 1a, 2a and difficult to enter therebetween, it is not effective for protecting the contacting surface and on the other hand, because a basic oil having a low viscosity is natured to easily enter the contact surface and form an oil film on the contact surface to protect the contact surface to protect the contact surface by preventing it from being fretted. A resistance against fretting property of the bearing at the time of non-rotation is available by applying the above oil of viscosity (15˜20 mm2/s), but, the life for maintaining the property is short and at the time of rotation of the bearing the oil is scattered from a boundary face by being stirred to lose lubrication.
The present invention has been made in the above circumstance and the object thereof is to provide a ball bearing having both properties of a fretting resistance at the time of non-rotation and being lubricated at the time of rotation, and a lubricating method thereof.
In order to attain the above object, according to a first aspect of the present invention, it is characterized by disposing a grease for protecting a lubricated surface of race portions and another grease for maintaining lubrication on a retainer portion.
By this arrangement, the lubricated surface formed in the bearing is protected by the grease for protecting the lubricated surface and the lubrication is maintained on the lubricated surface by the lubrication maintaining grease.
According to a second aspect of the present invention, a viscosity of a basic oil for protecting the lubricated surface is lower than a basic oil for maintaining the lubrication.
By setting as such, a quick entering of the grease for protecting the lubricated surface at non-rotation of the ball bearing into the contact surface of the race portions can be assured to protect the lubricated surface.
According to a third aspect of the present invention, the grease for protecting the lubricated surface and the grease for maintaining the lubrication are disposed close each other.
By setting as such, a lubricant separated from the grease for maintaining the lubrication can be supplied quickly to the lubricated surface.
Further, according to a fourth aspect of the present invention, the grease for protecting the lubricating of the lubricated face is a churning type of a basic oil viscosity of 15˜20 mm2/s and a worked penetration of 200˜230, and the grease for maintaining lubrication is of a channeling type of a basic oil viscosity of 25˜30 mm2/s and a worked penetration of 240˜270.
Further, according to a fifth aspect of the present invention, a grease for protecting the lubricated surface is disposed at race portions, and the grease for maintaining the lubrication by the grease for protecting the lubricated surface is disposed at a retainer portion, and the lubricated surface is formed at non-rotation of the ball bearing and the lubrication is maintained by the grease for maintaining the lubrication at rotation of the ball bearing.
By arranging as such, the lubricated surface can be maintained by the grease for maintaining the lubricated surface at the time of the rotation of the ball bearing and the lubricated surface is protected by the grease for protecting the lubricated surface to avoid the fretting at the contact surface at the time of no-rotation of the ball bearing.
Further, according to a sixth aspect of the present invention, the grease for protecting the lubricated surface and the grease for maintaining the lubrication are disposed close, and the lubrication is adapted to be maintained by supplying gradually the grease for maintaining to the lubricated surface at rotation of the ball bearing.
By arranging as such, the lubricant separated from the grease for maintaining the lubrication is supplied on the lubricating surface quickly at rotation, and even at the time of a high speed rotation of the ball bearing, the lubricated surface is maintained and the lubrication of the ball bearing can be continued.